Add gcloud.* and gcloud.datastore.* docstrings to pacify pylint.

See https://github.com/GoogleCloudPlatform/gcloud-python/pull/238#issuecomment-58954981.
From [PEP8][1]

> For one liner docstrings, please keep the closing `"""` on the same line.

[1]: http://legacy.python.org/dev/peps/pep-0008/#documentation-strings